U.S. patent application number 10/077950 was filed with the patent office on 2002-11-07 for laser cutting method and apparatus with a bifocal optical means and a hydrogen-based assist gas.
Invention is credited to Matile, Olivier.
Application Number | 20020162604 10/077950 |
Document ID | / |
Family ID | 8860955 |
Filed Date | 2002-11-07 |
United States Patent
Application |
20020162604 |
Kind Code |
A1 |
Matile, Olivier |
November 7, 2002 |
Laser cutting method and apparatus with a bifocal optical means and
a hydrogen-based assist gas
Abstract
Apparatus and method for cutting a workpiece by the use of a
laser beam and an assist gas, in which at least one optical means
is used to focus the laser beam at several focal points separate
from one another, and in which, as assist gas for the said laser
beam, a gas mixture containing hydrogen and at least one inert gas
is used. The optical means is transparent or reflecting and is
chosen from lenses, mirrors and combinations thereof, preferably a
bifocal lens. The workpiece to be cut is made of stainless steel,
coated steel, aluminum or an aluminum alloy, non-alloy steel or
alloy steel. The inert gas is chosen from nitrogen, argon, helium
and mixtures thereof.
Inventors: |
Matile, Olivier; (Paris,
FR) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET 2ND FLOOR
ARLINGTON
VA
22202
|
Family ID: |
8860955 |
Appl. No.: |
10/077950 |
Filed: |
February 20, 2002 |
Current U.S.
Class: |
148/194 ;
266/48 |
Current CPC
Class: |
B23K 26/0617 20130101;
B23K 2103/04 20180801; B23K 26/067 20130101; B23K 2103/05 20180801;
B23K 26/123 20130101; B23K 2103/50 20180801; B23K 2103/10 20180801;
B23K 26/125 20130101; B23K 26/40 20130101; B23K 26/064
20151001 |
Class at
Publication: |
148/194 ;
266/48 |
International
Class: |
B23K 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 9, 2001 |
FR |
0103265 |
Claims
1. Method for cutting a workpiece by using a laser beam and an
assist gas, in which at least one optical means is used to focus
the laser beam at several focal points, separate from one another,
and in which, as assist gas for the said laser beam, a gas mixture
containing hydrogen and at least one inert gas is used.
2. Method according to claim 1, characterized in that the optical
means is transparent or reflecting and is chosen from lenses,
mirrors and combinations thereof, preferably a bifocal lens.
3. Method according to either of claims 1 and 2, characterized in
that the workpiece to be cut is made of stainless steel, coated
steel, aluminium or aluminium alloy, non-alloy steel or alloy
steel.
4. Method according to one of claims 1 to 3, characterized in that
the inert gas is chosen from nitrogen, argon, helium and mixtures
thereof, preferably the inert gas being chosen from nitrogen, argon
and mixtures thereof.
5. Method according to one of claims 1 to 4, characterized in that
the assist gas contains from 150 ppm by volume to 40% by volume of
hydrogen, preferably from 0.5% by volume to 30% by volume of
hydrogen, the balance being the inert gas.
6. Method according to one of claims 1 to 5, characterized in that
the assist gas consists of 5% by volume to 30% by volume of
hydrogen, the balance being nitrogen.
7. Method according to one of claims 1 to 6, characterized in that
the thickness of the workpiece to be cut is between 0.2 mm and 20
mm, typically between 0.3 mm and 16 mm.
8. Method according to one of claims 1 to 7, characterized in that
the cutting speed is between 0.5 m/min and 20 m/min.
9. Method according to one of claims 1 to 8, characterized in that
the optical means is arranged so as to obtain at least one first
focal point positioned near the upper surface of the workpiece to
be cut, preferably so as to coincide with the said upper surface,
or in the thickness of the workpiece to be cut in a region close to
the said upper surface, and at least one second focal point
positioned near the lower surface of the workpiece to be cut and in
the thickness of the latter, or outside the latter.
10. Method according to one of claims 1 to 9, characterized in that
the assist gas contains hydrogen in an amount adjusted according to
the thickness and/or the constituent material of the workpiece to
be cut.
11. Laser beam cutting apparatus for implementing a method
according to one of claims 1 to 10, comprising: at least one laser
generator for generating at least one laser beam; at least one
cutting nozzle with at least one laser beam inlet and at least one
laser beam outlet; at least one transparent or reflecting optical
means of the multifocus type for focusing the said laser beam at
several focal points; and at least one source of assist gas
containing hydrogen and at least one inert gas for the said laser
beam and for feeding the said nozzle with the said assist gas.
12. Laser beam cutting apparatus for implementing a method
according to one of claims 1 to 10, comprising : at least one laser
generator for generating at least one laser beam; at least one
cutting nozzle with at least one laser beam inlet and at least one
laser beam outlet; at least one transparent or reflecting optical
means of the multifocus type for focusing the said laser beam at
several focal points; at least a first source of gas containing at
least hydrogen; at least a second source of gas containing at least
one inert gas; and gas mixing means for mixing the gas coming from
the first gas source with gas coming from the second gas source so
as to obtain an assist gas for the said laser beam containing
hydrogen and at least one inert gas, the said assist gas feeding
the said nozzle.
Description
[0001] The present invention relates to a method of cutting
stainless steels, coated steels, aluminium and its alloys,
non-alloy steels, alloy steels and high-alloy steels, whether they
be ferritic or austenitic, by laser beam using a lens or a mirror
having several focal points, to focus the laser beam at least two
points which are separate from one another and preferably lie on
the same axis, and a mixture of hydrogen and at least one inert
component, such as nitrogen, as assist gas for the laser beam.
[0002] Stainless steels, coated steels, aluminium and aluminium
alloys, non-alloy steels, alloy steels and high-alloy steels,
whether they be ferritic or austenitic, are especially cut by using
a laser beam and nitrogen or oxygen as assist gas for the laser
beam, that is to say as cutting gas.
[0003] Moreover, it is known that the use of nitrogen as cutting
gas for these materials results in cutting speeds which are
considerably less than those obtained with oxygen, typically 30 to
60% less, and in high gas consumption, typically 30 to 600% greater
depending on the material in question.
[0004] It has been shown moreover, especially by document EP-A-655
021, that nitrogen/hydrogen mixtures make it possible to increase
the cutting speed when laser cutting workpieces to be machined in
the form of strip or plate, especially in the form of sheet.
[0005] In other words, it is known to use mixtures of the
nitrogen/hydrogen type instead of nitrogen so as to improve the
performance of the laser cutting method compared with laser cutting
using pure nitrogen.
[0006] Moreover, document EP-A-886 555 proposes the use of
nitrogen/hydrogen or argon/hydrogen mixtures for laser cutting at
speeds of less than 10 m/min.
[0007] The problem that arises from the above is how to further
improve the methods for laser beam cutting of stainless steels,
coated steels, aluminium and aluminium alloys, non-alloy steels,
alloy steels and high-alloy steels, whether they be ferritic or
austenitic, so as to increase the cutting speed by at least 30 to
40% compared with a laser cutting method using pure nitrogen and by
at least 20% compared with a laser cutting method using a
nitrogen/hydrogen mixture, all other conditions being equal.
[0008] In addition, a further object of the invention is to
increase the performance of laser cutting methods, but while
controlling, or even reducing the amounts of assist gas consumed,
and do so in particular for the purpose of optimizing the overall
costs of the industrial cutting method used.
[0009] In other words, the object of the invention is therefore to
provide a laser cutting method which makes it possible to increase
the cutting performance and to limit the consumption of cutting
gas.
[0010] The present invention therefore relates to a method for
cutting a workpiece by using a laser beam and an assist gas, in
which at least one optical means is used to focus the laser beam at
several focal points, separate from one another, and in which, as
assist gas for the said laser beam, a gas mixture containing
hydrogen and at least one inert gas is used.
[0011] Depending on the case, the method of the invention may
include one or more of the following features:
[0012] the optical means of the multifocus type is chosen from
lenses, mirrors and combinations thereof, preferably a bifocal
lens, that is to say one which focuses the beam at two focal points
separate from each other. More generally, in the case of the
present invention, the term "optical means of the multifocus type"
is understood to mean an optical means allowing the laser beam to
be focused at several focal points separate from one another,
usually a first and a second focal point, which lie separately on
an axis approximately coaxial with the axis of the nozzle of the
laser device, that is to say of the laser head which emits the
laser beam or beams. Such an optical means and its use in laser
cutting are described in document EP-A-929 376;
[0013] the workpiece to be cut is chosen from plate, sheet and
tube;
[0014] the optical means is transparent or reflecting and is chosen
from lenses, mirrors and combinations thereof, preferably a bifocal
lens;
[0015] the workpiece to be cut is made of stainless steel, coated
steel, aluminium or aluminium alloy, non-alloy steel or alloy
steel;
[0016] the inert gas is chosen from nitrogen, argon, helium and
mixtures thereof, preferably the inert gas being chosen from
nitrogen, argon and mixtures thereof;
[0017] the assist gas contains from 150 ppm by volume to 40% by
volume of hydrogen, preferably from 0.5% by volume to 30% by volume
of hydrogen, the balance being the inert gas;
[0018] the assist gas consists of 5% by volume to 30% by volume of
hydrogen, the balance being nitrogen;
[0019] the thickness of the workpiece to be cut is between 0.2 mm
and 20 mm, typically between 0.3 mm and 16 mm;
[0020] the cutting speed is between 0.5 m/min and 20 m/min;
[0021] the optical means is arranged so as to obtain at least one
first focal point positioned near the upper surface of the
workpiece to be cut, preferably so as to coincide with the said
upper surface, or in the thickness of the workpiece to be cut in a
region close to the said upper surface, and at least one second
focal point positioned near the lower surface of the workpiece to
be cut and in the thickness of the latter, or outside the
latter;
[0022] the assist gas contains hydrogen in an amount adjusted
according to the thickness and/or the constituent material of the
workpiece to be cut.
[0023] The invention also relates to a laser beam cutting apparatus
for implementing a method according to the invention,
comprising:
[0024] at least one laser generator for generating at least one
laser beam;
[0025] at least one cutting nozzle with at least one laser beam
inlet and at least one laser beam outlet;
[0026] at least one transparent or reflecting optical means of the
multifocus type for focusing the said laser beam at several focal
points; and
[0027] at least one source of assist gas containing hydrogen and at
least one inert gas for the said laser beam and for feeding the
said nozzle with the said assist gas.
[0028] Alternatively, the laser beam cutting apparatus for
implementing a method according to the invention comprising:
[0029] at least one laser generator for generating at least one
laser beam;
[0030] at least one cutting nozzle with at least one laser beam
inlet and at least one laser beam outlet;
[0031] at least one transparent or reflecting optical means of the
multifocus type for focusing the said laser beam at several focal
points;
[0032] at least a first source of gas containing at least
hydrogen;
[0033] at least a second source of gas containing at least one
inert gas; and
[0034] gas mixing means for mixing the gas coming from the first
gas source with gas coming from the second gas source so as to
obtain an assist gas for the said laser beam containing hydrogen
and at least one inert gas, the said assist gas feeding the said
nozzle.
[0035] The invention relies on the use, in combination, on the one
hand, of one or more transparent or reflecting optical components,
such as lenses or mirrors, in order to obtain several separate
focal points (FP1, FP2, etc.) for the laser beam, lying
approximately along the same axis and, on the other hand, of a
mixture containing hydrogen and one or more inert gas components,
particularly nitrogen, argon or mixtures of these components, as
assist gas, that is to say as cutting gas.
[0036] A cutting apparatus that can be used to implement the
invention comprises, for example, a laser generator of the CO.sub.2
type for generating the laser beam, an output nozzle through which
the laser beam passes, at least one transparent or reflecting
optical means for focusing the said laser beam and a source of
assist gas for the laser beam, feeding the output nozzle with with
assist gas, the assist gas being introduced into the nozzle by, for
example, one or more gas inlets passing through the peripheral wall
of the nozzle. However, the laser may be of the Nd:YAG type.
[0037] According to the invention, a laser having a power of 500 to
6000 W is used.
[0038] The optical means is of the multifocus type, preferably a
bifocal lens, and the source of assist gas feeds the nozzle with an
assist gas mixture containing hydrogen and at least one inert
gas.
[0039] Transparent or reflecting optical components of this type,
that is to say those having several focal points, which can be used
within the context of the present invention are described in
document EP-A-929 376, to which reference may be made for further
details.
[0040] The principle of operation of a multifocus optical means is
outlined below.
[0041] A first focal point FP1 coming from the largest angle of
convergence obtained with the said multifocus optical means lies
near the upper surface of the workpiece to be cut, preferably so as
to coincide with the said upper surface, or in the thickness of the
material in a region close to the said upper surface.
[0042] Moreover, a second focal point FP2 coming from the smallest
angle of convergence obtained with the said multifocus optical
means lies near the lower surface of the workpiece in the thickness
of the material, or outside it.
[0043] This principle makes it possible, compared with the use of a
standard optical component, to use smaller nozzle diameters and
therefore to decrease the gas consumption, since such a standard
optical component, that is to say one having only a single focal
point, means positioning its single focal point, for which the
angle of convergence is the largest, at the lower face of the
material, or indeed below it, and, consequently, in order to allow
the laser beam through, it is necessary to use large-diameter
nozzles, which correspondingly increases the gas consumption.
COMPARATIVE EXAMPLES
[0044] To illustrate the invention, comparative trials were carried
out and the results of these trials, in terms of cutting speed, are
given in the table below.
[0045] A 3 mm thick stainless steel plate was cut with a CO.sub.2
laser having a power of 1500 W, using either pure nitrogen (Trial
1) or a gas mixture containing 25 vol. % H.sub.2, and nitrogen for
the balance, and this was done firstly, with a standard lens (Trial
2), that is to say one having a single focal point, and, secondly,
with a bifocal lens (Trial 3), all other operating conditions being
equal.
1 Comparative Table Trial 1 Trial 2 Trial 3 (prior art) (prior art)
(invention) Cutting gas Pure N.sub.2 N.sub.2 + 25% H.sub.2 N.sub.2
+ 25% H.sub.2 Optical Conventional Conventional Bifocal lens
component monofocal lens monofocal lens Cutting speed 2.2 m/min 2.5
m/min 3.2 m/min Gas consumption 15 m.sup.3/h 15 m.sup.3/h 10
m.sup.3/h
[0046] As may be seen in the table, Trial 3 according to the
invention results in markedly higher cutting speeds than those
obtained with the conventional methods (Trials 1 and 2), thanks to
the use, in combination, of a bifocal lens and an N.sub.2/H.sub.2
mixture, the H.sub.2 content of which was carefully controlled. The
same applies to the saving in gas consumption.
[0047] This is because the method of the invention makes it
possible to increase the cutting speed, under the conditions of the
above trials, by more than 40% with respect to a method using a
standard lens and pure nitrogen (Trial 1), and by more than 20%
compared with a method using a standard lens and a
nitrogen/hydrogen mixture (Trial 2).
[0048] In addition, it is also apparent from these trials that
Trial 3 is the one allowing the greatest saving of gas to be
made.
[0049] The proportion of H.sub.2 to be used is controlled or
adjusted according to various operating parameters, such as the
nature and/or the thickness of the material to be cut, especially
for the purpose of avoiding the formation of flash adhering to the
bottom of the kerf and/or the oxidation of the cutting faces by
oxygen or atmospheric air.
[0050] Preferably, the H.sub.2 contents are from 5% to 30% by
volume, the balance being nitrogen.
[0051] It is also conceivable to use argon instead of nitrogen, and
Ar+N.sub.2+H.sub.2 mixtures.
[0052] In summary, the use of a laser cutting method according to
the invention results in high cutting speeds, that is to say those
ranging from about 0.5 m/min to about 12 m/min, depending on the
thicknesses and on the material to be cut, combined with low
cutting gas flow rates, typically no more than 350 m.sup.3/h, and
the production of high-quality low-cost cut workpieces, in
particular with a laser source having a power of 1800 watts for
example.
* * * * *